Method of recording information in optical recording medium, information recording apparatus and optical recording medium

ABSTRACT

It is an object of the present invention to provide an information recording method for recording information in a data rewritable type optical recording medium having a plurality of information recording layers, which can form recording marks having good shapes. In the information recording method according to the present invention, a plurality of recording marks selected from a group consisting of several types of recording marks with different lengths are formed in an optical recording medium  10  having at least a stacked L 0  layer  20  and L 1  layer  30  by projecting a laser beam via a light incidence plane. In the case of forming at least one recording mark among the several types of recording marks in L 0  layer  20 , the recording powers of a top pulse T top  and a last pulse T lp  of the laser beam are set to Pw 0 ′ lower than the recording power Pw 0  of a multi-pulse T mp  thereof.

BACKGROUND OF THE INVENTION

The present invention relates to a method of recording information in anoptical recording medium, and particularly to a method of recordinginformation in a data rewritable type optical recording medium having aplurality of information recording layers. Further, the presentinvention relates to an information recording apparatus for recordinginformation in an optical recording medium, and particularly to aninformation recording apparatus for recording information in a datarewritable optical recording medium having a plurality of informationrecording layers. Furthermore, the present invention relates to anoptical recording medium, and particularly to a data rewritable opticalrecording medium.

DESCRIPTION OF THE PRIOR ART

Optical recording media typified by the CD and the DVD have been widelyused as recording media for recording digital data. The recordingcapacity demanded of such optical recording media has increased year byyear, and various proposals have been made to achieve this. One of theseproposals is a technique that uses a two-layer structure for theinformation recording layers contained in the optical recording media,which has found practical application in the DVD-Video and DVD-ROMformats which are read-only optical storage media. With such read-onlyoptical recording media, pre-pits formed on the substrate surface becomethe information recording layer, and such substrates have a laminatedstructure with an intervening intermediate layer.

In addition, in recent years, proposals have been made for opticalrecording media with a two-layer structure for the information recordinglayer to be used also as an optical recording medium in which data canbe rewritten (data rewritable type optical recording medium) (SeeJapanese Patent Application Laid Open NO. 2001-273638). Such a datarewritable type optical recording medium has a structure in which arecording film and dielectric films between which they are sandwichedform an information recording layer, and these information recordinglayers are laminated.

A phase change material is generally used for forming a recording filmof a data rewritable type optical recording medium and data are recordedutilizing the difference in the reflection coefficients between the casewhere the recording film is in a crystal phase and the case where it isin an amorphous phase. More specifically, in an unrecorded state,substantially the entire surface of the recording film is in a crystalphase and when data are recorded, the phase of a predetermined region ofthe recording film is changed to the amorphous phase to form a recordingpit. The phase of the phase change material in the crystal phase can bechanged to the amorphous phase by heating the phase change material to atemperature equal to or higher than the melting point thereof andquickly cooling it. On the other hand, the phase change material in theamorphous phase can be crystallized by heating the phase change materialto a temperature equal to or higher than the crystallization temperaturethereof and gradually cooling it.

Such heating and cooling can be performed by adjusting the power(output) of a laser beam. In other words, it is possible not only torecord data in an unrecorded recording film but also to directlyoverwrite (direct-overwrite) a recording mark already formed in a regionof the recording film with a different recording mark by modulating theintensity of the laser beam. Generally, the power of the laser beam ismodulated in accordance with a pulse waveform having an amplitudebetween a recording power (Pw) and a bottom power (Pb) in order to heatthe recording film to a temperature equal to or higher than the meltingpoint thereof and the power of the laser beam is set to the bottom power(Pb) in order to quickly cool the recording film. Further, in order toheat the recording film to a temperature equal to or higher than thecrystallization temperature thereof and gradually cool it, the power ofa laser beam is set to an erasing power (Pe). In this case, the erasingpower (Pe) is set to a level at which the recording film is heated to atemperature equal to or higher than the crystallization temperaturethereof and lower than the melting point thereof, thereby performingso-called solid phase erasing.

Here, in a data rewritable type optical recording medium having twoinformation recording layers, since data are recorded or reproduced byfocusing a laser beam onto one of the information recording layers, inthe case of recording data in or reproducing data from the informationrecording layer farther from the light incidence plane (hereinafterreferred to as an “L1 layer”), a laser beam is projected thereonto viathe information recording layer closer to the light incidence plane(hereinafter referred to as an “L0 layer”). Therefore, since it isnecessary for the L0 layer to have a sufficiently high lighttransmittance, it is general for the L0 layer to include no reflectivefilm or even if the L0 layer includes a reflective film, the thicknessof the reflective film is set to be very thin.

Since the L0 layer thus includes no reflective film or even if the L0layer includes a reflective film, the thickness of the reflective filmis set to be very thin in a data rewritable type optical recordingmedium having two information recording layers, the heat radiationcharacteristic of the L0 layer is lower than that of the L1 layerincluding a sufficiently thick reflective film and, therefore,re-crystallization of the phase change material tends to occur. Morespecifically, since metal is generally used as the material for forminga reflective film, heat generated in the L1 layer by irradiation with alaser beam can be quickly radiated through the reflective film havinghigh thermal conductivity but since the L0 layer includes no reflectivefilm or only a very thin reflective film, heat generated in the L0 layerby irradiation with a laser beam cannot be quickly radiated. A recordingmark (an amorphous region) formed in the L0 layer is therefore deformedand a good signal cannot be reproduced.

Particularly, in recent years, attempts have been made to record largequantities of data by setting the quotient (λ/NA) of the wavelength λ ofthe laser beam used for recording and/or reproducing divided by thenumerical aperture (NA) of the objective lens used to focus the laserbeam to be equal to or shorter than 700 nm, for example, by setting thenumerical aperture NA to 0.7 or greater, e.g. roughly 0.85, and alsoshortening the wavelength λ of the laser beam to about 200 to 450 nm inorder to make the focused spot diameter of the laser beam smaller andincrease the recording density. In such a system that records and/orreproduces data using a laser beam of short wavelength converged by anobjective lens having a high NA, the above mentioned influence ofthermal interference becomes great in the L0 layer and the phase changematerial tends to be re-crystallized. Further, cross-talk andcross-erase occur due to the presence of recording marks on neighboringtracks.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aninformation recording method for recording information in a datarewritable type optical recording medium having a plurality ofinformation recording layers, which can form recording marks having goodshapes.

Further, another object of the present invention is to provide aninformation recording apparatus for recording information in a datarewritable type optical recording medium having a plurality ofinformation recording layers, which can form recording marks having goodshapes.

Moreover, a further object of the present invention is to provide a datarewritable type optical recording medium having a plurality ofinformation recording layers, in which recording marks having goodshapes can be formed.

The above objects of the present invention can be accomplished by aninformation recording method for recording information in an opticalrecording medium having at least stacked first and second informationrecording layers where information is recorded by projecting apulse-like laser beam whose power is modulated between a plurality oflevels including at least a recording power onto the optical recordingmedium via a light incidence plane and forming thereon a plurality ofrecording marks selected from a group consisting of several types ofrecording marks with different lengths, the information recording methodcomprising a step of setting the recording powers of a top pulse and/ora last pulse of the laser beam used when information is to be recordedin the first information recording layer to be lower than the recordingpower of a multi-pulse thereof.

In a preferred aspect of the present invention, the first informationrecording layer is located on the side of the light incidence plane withrespect to the second information recording layer.

In a further preferred aspect of the present invention, information isrecorded in the second information recording layer with the recordingpowers of a top pulse and/or a last pulse of the laser beam set to besubstantially the same as the recording power of a multi-pulse thereof.

In a further preferred aspect of the present invention, the recordingpower of the top pulse and the recording power of the last pulse are setto be at the same level.

In a further preferred aspect of the present invention, a wavelength λof the laser beam and a numerical aperture NA of an objective lenssatisfy the condition that λ/NA is equal to or shorter than 700 nm.

In a further preferred aspect of the present invention, the laser beamhas a wavelength λ of 200 to 450 nm.

The above object of the present invention can be also accomplished by aninformation recording apparatus for recording information in an opticalrecording medium having at least stacked first and second informationrecording layers where information is recorded by projecting apulse-like laser beam whose power is modulated between a plurality oflevels including at least a recording power onto the optical recordingmedium via a light incidence plane and forming thereon a plurality ofrecording marks selected from a group consisting of several types ofrecording marks with different lengths, the information recordingapparatus being constituted so as to set the recording powers of a toppulse and/or a last pulse of the laser beam used when information is tobe recorded in the first information recording layer to be lower thanthe recording power of a multi-pulse thereof.

In a preferred aspect of the present invention, the first informationrecording layer is located on the side of the light incidence plane withrespect to the second information recording layer.

In a further preferred aspect of the present invention, information isrecorded in the second information recording layer with the recordingpowers of a top pulse and/or a last pulse of the laser beam set to besubstantially the same as the recording power of a multi-pulse thereof.

In a further preferred aspect of the present invention, a wavelength λof the laser beam and a numerical aperture NA of an objective lenssatisfy the condition that λ/NA is equal to or shorter than 700 nm.

In a further preferred aspect of the present invention, the laser beamhas a wavelength λ of 200 to 450 nm.

The above object of the present invention can be also accomplished by anoptical recording medium which has at least stacked first and secondinformation recording layers and in which information can be recorded byprojecting a pulse-like laser beam whose power is modulated between aplurality of levels including at least a recording power onto theoptical recording medium via a light incidence plane and forming thereona plurality of recording marks selected from a group consisting ofseveral types of recording marks with different lengths, the opticalrecording medium comprising setting information required for setting therecording powers of a top pulse and/or a last pulse of the laser beamused when information is to be recorded in the first informationrecording layer to be lower than the recording power of a multi-pulsethereof.

In a preferred aspect of the present invention, the first informationrecording layer is located on the side of the light incidence plane withrespect to the second information recording layer.

In a further preferred aspect of the present invention, information isrecorded in the second information recording layer with the recordingpowers of a top pulse and/or a last pulse of the laser beam set to besubstantially the same as the recording power of a multi-pulse thereof.

In a preferred aspect of the present invention, the optical recordingmedium further comprises a light transmission layer and the lighttransmission layer has a thickness of 30 to 200 μm.

According to the present invention, recording marks having good shapescan be formed even when information in any one of the informationrecording layers is directly overwritten.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section illustrating the structure of anoptical recording medium 10 according to a preferred embodiment of thepresent invention.

FIG. 2 is a drawing illustrating a part of a process (a step for forminga substrate 11) for manufacturing an optical recording medium 10.

FIG. 3 is a drawing illustrating a part of a process (a step for formingan L1 layer 30) for manufacturing an optical recording medium 10.

FIG. 4 is a drawing illustrating a part of a process (a step for forminga transparent intermediate layer 12) for manufacturing an opticalrecording medium 10.

FIG. 5 is a drawing illustrating a part of a process (a step for formingan L0 layer 20) for manufacturing an optical recording medium 10.

FIG. 6 is a set of waveform diagrams showing pulse train patterns usedfor recording data in an L1 recording film 32 wherein FIG. 6( a) shows acase of recording a 2T signal, FIG. 6( b) shows a case of recording a 3Tsignal, FIG. 6( c) shows a case of recording a 4T signal and FIG. 6( d)shows a case of recording one of a 5T signal to an 8T signal.

FIG. 7 is a set of waveform diagrams showing pulse train patterns usedfor recording data in an L0 recording film 22 wherein FIG. 6( a) shows acase of recording a 2T signal, FIG. 6( b) shows a case of recording a 3Tsignal, FIG. 6( c) shows a case of recording a 4T signal and FIG. 6( d)shows a case of recording one of a 5T signal to an 8T signal.

FIG. 8 is a schematic drawing of the major components of an informationrecording apparatus 50 for recording data in an optical recording medium10.

FIG. 9 is a graph showing the results of single jitter measurement.

FIG. 10 is a graph showing the results of cross jitter measurement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be explained indetail with reference to the drawings.

FIG. 1 is a schematic cross section illustrating the structure of anoptical recording medium 10 according to a preferred embodiment of thepresent invention.

As shown in FIG. 1, an optical recording medium 10 according to thisembodiment includes a substrate 11, an intermediate layer 12, a lighttransmission layer 13, an L0 layer 20 provided between the intermediatelayer 12 and the light transmission layer 13 and an L1 layer 30 providedbetween the substrate 11 and the intermediate layer 12. The L0 layer 20constitutes an information recording layer far from a light incidenceplane 13 a and is constituted by a first dielectric film 21, an L0recording film 22 and a second dielectric film 23. Further, the L1 layer30 constitutes an information recording layer close to the lightincidence plane 13 a and is constituted by a third dielectric film 31,an L1 recording film 32 and a fourth dielectric film 33. In this manner,the optical recording medium 10 according to this embodiment includestwo information recording layers (the L0 layer 20 and the L1 layer 30).

The substrate 11 is a disc-like substrate having a thickness of about1.1 mm serving as a support for ensuring mechanical strength requiredfor the optical recording medium 10 and grooves 11 a and lands 11 b areformed on the surface thereof. The grooves 11 a and/or lands 11 b serveas a guide track for the laser beam L when data are to be recorded inthe L1 layer 30 or when data are to be reproduced from the L1 layer 30.Although the depth of the groove 11 a is not particularly limited, it ispreferably set to 10 nm to 40 nm and the pitch of the grooves 11 a ispreferably set to 0.2 μm to 0.4 μm. Various materials can be used forforming the substrate 11 and the substrate 11 can be formed of glass,ceramic, resin or the like. Among these, resin is preferably used forforming the substrate 11 since resin can be easily shaped. Illustrativeexamples of resins suitable for forming the substrate 11 includepolycarbonate resin, olefin resin, acrylic resin, epoxy resin,polystyrene resin, polyethylene resin, polypropylene resin, siliconeresin, fluoropolymers, acrylonitrile butadiene styrene resin, urethaneresin and the like. Among these, polycarbonate resin or olefin resin ismost preferably used for forming the substrate 11 from the viewpoint ofeasy processing, optical characteristics and the like. In thisembodiment, since the laser beam L does not pass through the substrate11, it is unnecessary for the substrate 11 to have a light transmittanceproperty.

The intermediate layer 12 serves to space the L0 layer 20 and the L1layer 30 apart by a sufficient distance and grooves 12 a and lands 12 bare formed on the surface thereof. The grooves 12 a and/or lands 12 bserve as a guide track for the laser beam L when data are to be recordedin the L0 layer 20 or when data are to be reproduced from the L0 layer20. The depth of the groove 12 a and the pitch of the grooves 12 a canbe set to be substantially the same as those of the grooves 11 a formedon the surface of the substrate 11. The depth of the intermediate layer12 is preferably set to be 10 μm to 50 μm. The material for forming theintermediate layer 12 is not particularly limited and an ultraviolet raycurable acrylic resin is preferably used for forming the intermediatelayer 12. It is necessary for the transparent intermediate layer 12 tohave sufficiently high light transmittance since the laser beam L passesthrough the transparent intermediate layer 12 when data are to berecorded in the L1 layer 30 and data recorded in the L1 layer 30 are tobe reproduced.

The light transmission layer 13 forms an optical path of a laser beamand a light incident plane 13 a is constituted by one of the surfacesthereof. The thickness of the light transmission layer 13 is preferablyset to be 30 μm to 200 μm. The material for forming the lighttransmission layer 13 is not particularly limited and, similarly to theintermediate layer 12, an ultraviolet ray curable acrylic resin ispreferably used for forming the light transmission layer 13. Asdescribed above, it is necessary for the light transmission layer 13 tohave sufficiently high light transmittance since the laser beam L passesthrough the transparent intermediate layer 13.

Each of the L0 recording film 22 and the L1 recording film 33 is formedof a phase change material. Utilizing the difference in the reflectioncoefficients between the case where the L0 recording film 22 and the L1recording film 33 are in a crystal phase and the case where they are inan amorphous phase, data are recorded in the L0 recording film 23 andthe L1 recording film 33. The material for forming the L0 recording film22 and the L1 recording film 33 is not particularly limited but it ispreferable to form them using a SbTe system material. As the SbTe systemmaterial, SbTe may be used alone, or InSbTeGe, AgInSbTe, Ag SbTeGe,AgInSbTeGe or the like containing In, Te, Ge, Ag or the like asadditives may be used.

Since the laser beam passes through the L0 recording film 22 when dataare recorded in the L1 layer 30 and data recorded in the L1 layer 30 arereproduced, it is necessary for the L0 layer 20 to have a high lighttransmittance. Therefore, the thickness of the L0 recording film 22 isset to be considerably thinner than that of the L1 recording film 32.Concretely, it is preferable to set the thickness of the L1 recordingfilm 32 to be about 3 to 20 nm and the thickness of the L0 recordingfilm 22 to be 0.3 to 0.8 times that of the L1 recording film 32.

The first dielectric film 21 and the second dielectric film 23 formed soas to sandwich the L0 recording film 22 serve as protective films forthe L0 recording film 22 and the third dielectric film 31 and the fourthdielectric film 33 formed so as to sandwich the L1 recording film 32serve as protective films for the L10 recording film 32. The thicknessof the first dielectric film 21 is preferably set to be 2 to 200 nm, thethickness of the second dielectric film 23 is preferably set to be 2 to200 nm, the thickness of the third dielectric film 31 is preferably setto be 2 to 200 nm and the thickness of the fourth dielectric film 33 ispreferably set to be 2 to 200 nm.

Each of these dielectric films may have a single-layered structure ormay have a multi-layered structure including a plurality of dielectricfilms. The material for forming each of these dielectric films is notparticularly limited but it is preferable to form it of oxide, nitride,sulfide, carbide of Si, Al, Ta and Zn such as SiO₂, Si₃O₄, Al₂O₃, AlN,TaO, ZnS, CeO₂ and the like or a combination thereof.

The reflective film 34 serves to reflect the laser beam entering throughthe light incident plane 13 a so as to emit it from the light incidentplane 13 a and the thickness thereof is preferably set to be 20 to 200nm. The material for forming the reflective film 34 is not particularlylimited but the reflective film 34 is preferably formed of an alloycontaining Ag or Al as a primary component and may be formed of Au, Ptor the like. Further, a moisture proof film may be provided between thereflective film 34 and the substrate 11 in order to prevent thereflective film 34 from being corroded. Materials usable for formingeach of the first dielectric film 21 to the fourth dielectric film 33can be used for forming the moisture proof film. Further, although theL0 layer 20 includes no reflective film, a thin reflective film having athickness of about 3 to 15 nm may be provided in the L0 layer 20. Inthis case, the reflective film can be formed of the same material asused for forming the reflective film 34.

When data recorded in the thus constituted optical recording medium 10are reproduced, a laser beam having a wavelength of 200 to 450 nm isprojected onto the optical recording medium 10 via the light incidenceplane 13 a and the amount of the laser beam reflected from the opticalrecording medium 10 is detected. As described above, since the L0recording film 22 and the L1 recording film 32 are formed of the phasechange material and the reflection coefficient in the case where thephase change material is in the crystal phase and that in the case whereit is in the amorphous phase are different from each other, it ispossible to judge by projecting the laser beam via the light incidenceplane 13 a, focusing it onto one of the L0 recording film 22 and the L1recording film 32 and detecting the amount of the laser beam reflectedtherefrom whether a region of the L0 recording film 22 or the L1recording film 32 irradiated with the laser beam is in the crystal phaseor the amorphous phase.

When data are to be recorded in the optical recording medium 10, a laserbeam having a wavelength of 200 to 450 nm is projected to be focusedonto one of the L0 recording film 22 and the L1 recording film 32 and inaccordance with data to be recorded therein, a predetermined region ofone of the L0 recording film 22 and the L1 recording film 32 is heatedto a temperature equal to or higher than the melting point thereof andquickly cooled, thereby changing the phase thereof to the amorphousphase or a predetermined region of one of the L0 recording film 22 andthe L1 recording film 32 is heated to a temperature equal to or higherthan the crystallization temperature and gradually cooled, therebychanging the phase thereof to the crystal phase. The region whose phasehas been changed to the amorphous phase is referred to as “a recordingmark” and recorded data are expressed by the length from the startingpoint of the recording mark to the ending point thereof and the lengthfrom the ending point thereof to the starting point of the nextrecording mark. The length of each recording mark and the length betweenrecording marks (edge to edge) are set to one of the lengthscorresponding to 2T through 8T (where T is the clock period) whenadopting the (1, 7) RLL modulation scheme, although this is noparticular limitation. A pulse train pattern used for recording data inthe L0 recording film 22 and a pulse train pattern used for recordingdata in the L1 recording film 32 will be described later.

When recording data in or reproducing data from the L1 layer 30, a laserbeam is projected onto the L1 recording film 32 via the L0 layer 20.Therefore, it is necessary for the L0 layer 20 to have a high lighttransmittance and, as pointed out above, the thickness of the L0recording film 22 is set to be considerably thinner than that of the L1recording film 32.

Here follows a description of the method of manufacturing an opticalrecording medium 10 according to this preferred embodiment.

FIGS. 2 to 5 are step drawings illustrating the method of manufacturingthe optical recording medium 10.

First, as shown in FIG. 2, a stamper 40 is used to perform injectionmolding of a substrate 11 having grooves 11 a and lands 11 b. Next, asshown in FIG. 5, the sputtering method is used to form, upon nearly theentire surface of the side of the substrate 11 on which the grooves 11 aand the lands 11 b are formed, a reflective film 34, a fourth dielectricfilm 33, an L1 recording film 32 and a third dielectric film 34 in thisorder, thereby forming an L1 layer 30. Here, the phase of the L1recording film 32 is normally in an amorphous phase immediately afterthe sputtering is completed.

Next, as shown in FIG. 4, ultraviolet curable acrylic resin isspin-coated onto the L1 layer 30, and by shining an ultraviolet raythrough a stamper 41 in the state with its surface covered with thestamper 41, an intermediate layer 12 having grooves 12 a and lands 12 bis formed. Next, as shown in FIG. 7, the sputtering method is used toform, upon nearly the entire surface of the intermediate layer 12 onwhich the grooves 11 a and the lands 11 b are formed, a seconddielectric film 23, an L0 recording film 22 and a first dielectric film21 in this order. Thus, an L0 layer 20 is completed. Here, the phase ofthe L0 recording film 22 is normally in an amorphous phase immediatelyafter the sputtering is completed.

Moreover, as shown in FIG. 1, ultraviolet curable acrylic resin isspin-coated onto the L0 layer 20, and by shining an ultraviolet ray, alight transmission layer 13 is formed. This completes all filmdeposition steps. In this specification, the optical recording medium inthe state with the film deposition steps complete may also be called the“optical recording medium precursor.”

Next, the optical recording medium precursor is placed upon the rotarytable of a laser irradiation apparatus (not shown) and rotated whilebeing continuously irradiated with a rectangular laser beam having ashorter length in the direction along the track and a longer length inthe direction perpendicular to the track. By shifting the irradiationposition in the direction perpendicular to the track each time theoptical recording medium precursor makes one revolution, the rectangularlaser beam can be shined over nearly the entire surface of the L0recording film 22 and the L1 recording film 32. Thereby, the phasechange material making up the L0 recording film 22 and the L1 recordingfilm 32 is heated to a temperature equal to or higher than thecrystallization temperature thereof and then cooled slowly, so theentire surface of the L0 recording film 22 and the L1 recording film 32is put into the crystalline state, namely the unrecorded state. Thisprocess is called “an initializing process” in this specification.

When the initializing process is completed, the optical recording medium10 is competed.

As described above, it is possible to record the desired digital dataonto an optical recording medium 10 thus manufactured by aligning thefocus of the laser beam during recording to either the L0 recording film22 or the L1 recording film 32 to form recording marks. In addition,when data is recorded onto the L0 recording film 22 and/or L1 recordingfilm 32 of the optical recording medium 10 in this manner, as describedabove, by aligning the focus of a laser beam set to playback power toeither the L0 recording film 22 or the L1 recording film 32 anddetecting the amount of light reflected, it is possible to reproduce thedigital data thus recorded.

Next, a pulse train pattern used for recording data in the L0 recordingfilm 22 and a pulse train pattern used for recording data in the L1recording film 32 will be described in detail.

As described above, although the L1 layer 30 has a high heat radiationcharacteristic since it is provided with the reflective film 34 havinghigh thermal conductivity, the heat radiation characteristics of the L0layer 20 is low because the L0 layer 20 is provided with no reflectivefilm or, even if provided with a reflective film, is provided with onlya very thin reflective film, whereby the L0 recording film 22 tends tobe re-crystallized due to thermal interference. Therefore, in thepresent invention, different pulse train patterns are used between thecase of recording data in the L0 recording film 22 and the case ofrecording data in the L1 recording film 32, thereby reducing thermalinterference in the L0 recording film 22 in which the cooling effect islow.

Hereinafter, pulse train patterns in the case where the (1, 7)RLLmodulation scheme is selected will be concretely described. Although thedetails thereof will be described later, in this embodiment, in the caseof recording data in the L1 recording film 32, the recording power Pw ofthe laser beam is set to Pw1 (this recording format will be sometimesreferred to as “one value recording” hereinafter), and in the case ofrecording data in the L0 recording film 22, the recording power Pw ofthe laser beam is set to Pw0 or Pw0′ (this recording format will besometimes referred to as “double value recording” hereinafter).

FIG. 6 is a set of waveform diagrams showing pulse train patterns usedfor recording data in an L1 recording film 32 wherein FIG. 6( a) shows acase of recording a 2T signal, FIG. 6( b) shows a case of recording a 3Tsignal, FIG. 6( c) shows a case of recording a 4T signal and FIG. 6( d)shows a case of recording one of a 5T signal to an 8T signal.

As shown in FIGS. 6( a) to (d), in this embodiment, when data are to berecorded in the L1 recording film 32, the power of the laser beam ismodulated between three levels (three values) of a recording power(Pw1), an erasing power (Pe1) and a bottom power (Pb1). The level of therecording power (Pw1) is set to such a high level that the L1 recordingfilm 32 can be melted by the irradiation with the laser beam of therecording power Pw1. The level of the erasing power (Pe1) is set to sucha level that the L1 recording film 32 can be heated to a temperatureequal to or higher than a crystallization temperature thereof. The levelof the bottom power (Pb1) is set to such a low level that the melted L1recording film 32 can be cooled even if it is irradiated with the laserbeam of the bottom power Pb0.

The recording power (Pw1), the erasing power (Pe1) and the bottom power(Pb1) can be set in accordance with the configuration of the opticalrecording medium and the optical system of the information recordingapparatus. For example, the recording power (Pw1) can be set to 7.0 mWto 10.0 mW, the erasing power (Pe1) can be set to 4.0 mW to 7.0 mW andthe bottom power (Pb1) can be set to 0.1 mW to 0.5 mW. Here, the valuesof the recording power (Pw1), the erasing power (Pe1) and the bottompower (Pb1) are defined as those at the surface of an optical recordingmedium.

When recording marks are formed in the L1 recording film 32, namely,when the phase of the L1 recording film 32 is changed to the amorphousphase, the power of the laser beam is modulated in accordance with awaveform having the amplitude of the recording power (Pw1) or anamplitude between the recording power (Pw1) and the bottom power (Pb1)to heat the L1 recording film 32 to a temperature equal to or higherthan the melting point thereof, whereafter it is quickly cooled bysetting the power of the laser beam to the bottom power (Pb1). On theother hand, when the recording mark is to be erased, namely, when the L1recording film 32 is to be crystallized, the power of the laser beam isfixed at the erasing power (Pe1), thereby heating the L1 recording film32 to a temperature equal to or higher than the crystallizationtemperature thereof and lower than the melting point thereof andgradually cooling the L1 recording film 32. Thus, the recording mark issolid-phase erased. Hereinafter, concrete pulse train patterns for therespective recording marks will be described in detail.

First, as shown in FIG. 6( a), in the case of recording a 2T signal inthe L1 recording film 32, the number pulses is set to 1 and a coolinginterval T_(cl) is inserted thereafter. In the case of recording data inthe L1 recording film 32, the number of pulses is defined as the numberof times the power of the laser beam is raised to the recording power(Pw1). Further, in this specification, a first pulse is defined as a toppulse, a final pulse is defined as a last pulse and any pulse presentbetween the top pulse and the last pulse is defined as a multi-pulse.However, in the case where the number of pulses is set to 1 as shown inFIG. 6( a), the pulse is the top pulse.

At the cooling interval T_(cl), the power of the laser beam is set tothe bottom power (Pb1). In this manner, in this specification, a lastinterval during which the power of the laser beam is set to the bottompower (Pb1) is defined as the cooling interval. Therefore, in the caseof recording a 2T signal, the power of the laser beam is set to theerasing power (Pe1) before the time t₁₁, set to the recording power(Pw1) during the period (T_(top)) from the time t₁₁ to the time t₁₂, setto the bottom power (Pb1) during the period (T_(cl)) from the time t₁₂to the time t₁₃ and set to the erasing power (Pe1) after the time t₁₃.

Here, although the pulse width T_(top) of the top pulse is notparticularly limited, it is preferable to set it to 0.3T to 0.5T andparticularly preferable to set it to about 0.4T. Further, although thecooling interval T_(cl) is not particularly limited, it is preferable toset it to 0.6T to 1.0T and particularly preferable to set it to about0.8T.

Further, as shown in FIG. 6( b), in the case of recording a 3T signal inthe L1 recording film 32, the number of pulses of a laser beam is set to2 and a cooling interval T_(cl) is inserted thereafter. Therefore, inthe case of recording a 3T signal, the power of the laser beam is set tothe erasing power (Pe1) before the time t₂₁, set to the recording power(Pw1) during the period (T_(top)) from the time t₂₁, to the time t₂₂ andthe period (T_(lp)) from the time t₂₃ to the time t₂₄, set to the bottompower (Pb1) during the period (T_(off)) from the time t₂₂ to the timet₂₃ and the period (T_(cl)) from the time t₂₄ to the time t₂₅ and set tothe erasing power (Pe1) after the time t₂₅.

Here, although the pulse width T_(top) of the top pulse is notparticularly limited, it is preferable to set it to 0.3T to 0.5T andparticularly preferable to set it to about 0.4T. Further, although thepulse width T_(lp) of the last pulse is not particularly limited, it ispreferable to set it to 0.4T to 0.6T and particularly preferable to setit to about 0.5T. Moreover, although the off interval T_(off) is notparticularly limited, it is preferable to set it to (1—Tnxt). Here, Tnxtis the pulse width of a pulse present immediately before the offinterval T_(off) and corresponds to the pulse width T_(lp) of the toppulse in FIG. 6( b). Therefore, if T_(top) is equal to 0.4, the offinterval T_(off) is equal to 0.6. Further, although the cooling intervalT_(cl) is not particularly limited, it is preferable to set it to 0.6Tto 1.0T and particularly preferable to set it to about 0.8T.

Furthermore, as shown in FIG. 6( c), in the case of recording a 4Tsignal in the L1 recording film 32, the number of pulses of the laserbeam is set to 3 and a cooling interval T_(cl), is inserted thereafter.Therefore, in the case of recording a 4T signal, the power of the laserbeam is set to the erasing power (Pe1) before the time t₃₁, set to therecording power (Pw1) during the period (T_(top)) from the time t₃₁ tothe time t₃₂, the period (T_(mp)) from the time t₃₃ to the time t₃₄ andthe period (T_(lp)) from the time t₃₅ to the time t₃₆, set to the bottompower (Pb1) during the period (T_(off)) from the time t₃₂ to the timet₃₃, the period (T_(off)) from the time t₃₄ to the time t₃₅ and theperiod (T_(cl)) from the time t₃₆ to the time t₃₇ and set to the erasingpower (Pe1) after the time t₃₇.

Here, although the pulse width T_(top) of the top pulse and the pulsewidth T_(mp) of the multi-pulse are not particularly limited, it ispreferable to set them to 0.3T to 0.5T and particularly preferable toset them to about 0.4T. Further, although the pulse width T_(lp) of thelast pulse is not particularly limited, it is preferable to set it to0.4T to 0.6T and particularly preferable to set it to about 0.5T.Moreover, although the off interval T_(off) is not particularly limited,it is preferable to set it to (1—Tnxt). Here, Tnxt is the pulse width ofa pulse present immediately before the off interval T_(off) andcorresponds to the pulse width T_(top) of the top pulse or the pulsewidth T_(mp) of the multi-pulse in FIG. 6( c). Therefore, if T_(top) isequal to 0.4, the off interval T_(off) is equal to 0.6 and if T_(mp) isequal to 0.4, the off interval T_(off) is equal to 0.6. Further,although the cooling interval T_(cl) is not particularly limited, it ispreferable to set it to 0.6T to 1.0T and particularly preferable to setit to about 0.8T.

In addition, as shown in FIG. 6( d), in the case of recording any one ofa 5T signal to an 8T signal in the L1 recording film 32, the number ofpulses is correspondingly set to one of 4 to 7 and a cooling intervalT_(cl) is inserted thereafter. Therefore, in the case of recording anyone of a 5T signal to an 8T signal in the L1 recording film 32, thepower of the laser beam is set to the erasing power (Pe1) before thetime t₄₁, set to the recording power (Pw1) during the period (T_(top))from the time t₄₁ to the time t₄₂, the period (T_(mp)) from the time t₄₃to the time t₄₄, the period (T_(mp)) from the time t₄₅ to the time t₄₆and the period (T_(lp)) from the time t₄₇ to the time t₄₈, set to thebottom power (Pb1) during the period (T_(off)) from the time t₄₂ to thetime t₄₃, the period (T_(off)) from the time t₄₆ to the time t₄₇ and thecooling interval T_(cl) from the time t₄₈ to the time t₄₉, and set tothe erasing power (Pe1) after the time t₄₉.

Here, although the pulse width T_(top) of the top pulse and the pulsewidth T_(mp) of the multi-pulse are not particularly limited, it ispreferable to set them to 0.3T to 0.5T and particularly preferable toset them to about 0.4T. Further, although the pulse width T_(lp) of thelast pulse is not particularly limited, it is preferable to set it to0.4T to 0.6T and particularly preferable to set it to about 0.5T.Moreover, although the off interval T_(off) is not particularly limited,it is preferable to set it to (1—Tnxt). Here, Tnxt is the pulse width ofa pulse present immediately before the off interval T_(off) andcorresponds to the pulse width T_(top) of the top pulse or the pulsewidth T_(mp) of each of the multi-pulses in FIG. 6( d). Therefore, ifT_(top) is equal to 0.4, the off interval T_(off) is equal to 0.6 and ifT_(mp) is equal to 0.4, the off interval T_(off) is equal to 0.6.Further, although the cooling interval T_(cl) is not particularlylimited, it is preferable to set it to 0.6T to 1.0T and particularlypreferable to set it to about 0.8T.

Thus, at a region where one of recording signals among a 2T signal to an8T signal is to be recorded, the L0 recording film 22 or the L1recording film 32 melted by the irradiation with the laser beam of therecording power (Pw1) is quickly cooled during the cooling intervalT_(cl) and the phase thereof is changed to an amorphous phase. On theother hand, at the other regions, the L0 recording film 22 or the L1recording film 32 is heated to a temperature equal to or higher than thecrystallization temperature thereof and gradually cooled as the laserbeam is moved away, thereby being crystallized.

The pulse train patterns described above are those used for recordingdata in the L1 recording film 32. In this manner, in this embodiment, inthe case of recording data in the L1 recording film 32 far from thelight incidence plane 13 a, since the recording powers of the top pulse,the multi-pulses and the last pulse are equally set to Pw1, it ispossible to form recording marks having good shapes.

Next, pulse train patterns used for recording data in the L0 recordingfilm 22 will be described.

FIG. 7 is a set of waveform diagrams showing pulse train patterns usedfor recording data in the L0 recording film 22 wherein FIG. 7( a) showsa case of recording a 2T signal, FIG. 7( b) shows a case of recording a3T signal, FIG. 7( c) shows a case of recording a 4T signal and FIG. 7(d) shows a case of recording one of a 5T signal to an 8T signal.

As shown in FIGS. 7( a) to (d), in this embodiment, when data are to berecorded in the L1 recording film 32, the power of the laser beam ismodulated between four levels (four values) of a recording power (Pw0),a recording power (Pw0′), an erasing power (Pe0) and a bottom power(Pb0). The recording powers (Pw0) and (Pb0′) are set to such a highlevel that the L0 recording film 22 can be melted by irradiation withthe laser beam, the erasing power (Pe0) is set to such a level that theL0 recording film 22 can be heated by irradiation with the laser beam toa temperature equal to or higher than the crystallization temperaturethereof and lower than the melting point thereof, and the bottom power(Pb0) is set to such a low level that the melted L0 recording film 22can be cooled even if it is irradiated with the laser beam.

The recording power (Pw0), the recording power (Pb0′), the erasing power(Pe0) and the bottom power (Pb0) can be set in accordance with theconfiguration of the optical recording medium and the optical system ofthe information recording apparatus. For example, the recording power(Pw0) can be set to 5.0 mW to 6.6 mW, the erasing power (Pe0) can be setto 1.3 mW to 1.7 mW and the bottom power (Pb0) can be set to 0.1 mW to0.5 mW. The recording power (Pb0′) can be set to be lower than therecording power (Pw0), for example, about 0.9 times the recording power(Pw0) (0.9×Pw0). Here, the values of the recording power (Pw0), therecording power (Pb0′), the erasing power (Pe0) and the bottom power(Pb0) are defined as those at the surface of an optical recordingmedium.

When a recording mark is formed in the L0 recording film 22, namely,when the phase of the L0 recording film 22 is changed to the amorphousphase, the power of the laser beam is modulated in accordance with awaveform having the amplitude of the recording power (Pw0) or anamplitude between the recording power (Pw0) and the bottom power (Pb0)or a waveform having the amplitude of the recording power (Pb0′) or anamplitude between the recording power (Pb0′) and the bottom power (Pb0)to heat the L0 recording film 22 to a temperature equal to or higherthan the melting point thereof, whereafter it is quickly cooled bysetting the power of the laser beam to the bottom power (Pb0). On theother hand, when the recording mark formed in the L0 recording film 22is to be erased, namely, when the L0 recording film 22 is to becrystallized, the power of the laser beam is fixed at the erasing power(Pe0), thereby heating the L0 recording film 22 to a temperature equalto or higher than the crystallization temperature thereof and lower thanthe melting point thereof and gradually cooling the L0 recording film22. Thus, the recording mark is solid-phase erased. Hereinafter,concrete pulse train patterns for the respective recording marks will bedescribed in detail.

First, as shown in FIG. 7( a), in the case of recording a 2T signal inthe L0 recording film 22, the number of pulses is set to 1 and a coolinginterval T_(cl) is inserted thereafter. Here, the number of pulses isdefined as the number of times the power of the laser beam is raised tothe recording power (Pw0) or (Pw0′).

At the cooling interval T_(cl), the power of a laser beam is set to thebottom power (Pb0). In this manner, in this specification, in the caseof recording a 2T signal in the L0 recording film 22, a last intervalduring which the power of the laser beam is set to the bottom power(Pb0) is defined as the cooling interval. Therefore, in the case ofrecording a 2T signal in the L0 recording film 22, the power of thelaser beam is set to the erasing power (Pe0) before the time t₅₁, set tothe recording power (Pw0) during the period (T_(top)) from the time t₅₁to the time t₅₂, set to the bottom power (Pb0) during the period(T_(cl)) from the time t₅₂ to the time t₅₃ and set to the erasing power(Pe0) after the time t₅₃.

Here, although the pulse width T_(top) of the top pulse is notparticularly limited, it is preferable to set it to 0.2T to 0.4T andparticularly preferable to set it to about 0.3T. Further, although thecooling interval T_(cl) is not particularly limited, it is preferable toset it to 0.8T to 1.2T and particularly preferable to set it to about1.0T.

Further, as shown in FIG. 7( b), in the case of recording a 3T signal inthe L0 recording film 22, the number of pulses is set to 2 and a coolinginterval T_(cl), is inserted thereafter. Therefore, in the case ofrecording a 3T signal in the L0 recording film 22, the power of thelaser beam is set to the erasing power (Pe0) before the time t₆₁, set tothe recording power (Pw0) during the period (T_(top)) from the time t₆₁to the time t₆₂ and the period (T_(lp)) from the time t₆₃ to the timet₆₄, set to the bottom power (Pb0) during the period (T_(off)) from thetime t₆₂ to the time t₆₃ and the period (T_(cl)) from the time t₆₄ tothe time t₆₅, and set to the erasing power (Pe0) after the time t₆₅.

Here, although the pulse width T_(top) of the top pulse and the pulsewidth T_(lp) of the last pulse are not particularly limited, it ispreferable to set them to 0.15T to 0.3T and particularly preferable toset them to 0.2T. Further, although the off interval T_(off) is notparticularly limited, it is preferable to set it to (1—Tnxt). Here, Tnxtis the pulse width of a pulse present immediately before the offinterval T_(off) and corresponds to the pulse width T_(lp) of the toppulse in FIG. 7( b). Therefore, if T_(lp) is equal to 0.2, the offinterval T_(off) is equal to 0.8. Further, although the cooling intervalT_(cl) is not particularly limited, it is preferable to set it to 0.8Tto 1.2T and particularly preferable to set it to about 1.0T.

Furthermore, as shown in FIG. 7( c), in the case of recording a 4Tsignal in the L0 recording film 22, the number of pulses is set to 3 anda cooling interval T_(cl) is inserted thereafter. Therefore, in the caseof recording a 4T signal in the L0 recording film 22, the power of thelaser beam is set to the erasing power (Pe0) before the time t₇₁, set tothe recording power (Pw0′) during the period (T_(top)) from the time t₇₁to the time t₇₂ and the period (T_(lp)) from the time t₇₅ to the timet₇₆, set to the recording power (Pw0) during the period (T_(mp)) fromthe time t₇₃ to the time t₇₄, set to the bottom power (Pb0) during theperiod (T_(off)) from the time t₇₂ to the time t₇₃, the period (T_(off))from the time t₇₄ to the time t₇₅ and the period (T_(cl)) from the timet₇₆ to the time t₇₇, and set to the erasing power (Pe0) after the timet₇₇.

Here, although the pulse width T_(top) of the top pulse, the pulse widthT_(mp) of the multi-pulse and the pulse width T_(lp) of the last pulseare not particularly limited, it is preferable to set them to 0.15T to0.3T and particularly preferable to set them to 0.2T. Further, althoughthe off interval T_(off) is not particularly limited, it is preferableto set it to (1—Tnxt). Here, Tnxt is the pulse width of a pulse presentimmediately before the off interval T_(off) and corresponds to the pulsewidth T_(top) of the top pulse or the pulse width T_(mp) of themulti-pulse in FIG. 7( c). Therefore, if T_(top) is equal to 0.2, theoff interval T_(off) is equal to 0.8 and if T_(mp) is equal to 0.2, theoff interval T_(off) is equal to 0.8. Further, although the coolinginterval T_(cl) is not particularly limited, it is preferable to set itto 0.8T to 1.2T and particularly preferable to set it to about 1.0T.

In addition, as shown in FIG. 7( d), in the case of recording any one ofa 5T signal to an 8T signal in the L0 recording film 22, the number ofpulses is correspondingly set to one of 4 to 7 and a cooling intervalT_(cl) is inserted thereafter. The number of multi-pulses is set to 2 to5 correspondingly to a 5T signal to an 8T signal. In this case, thepower of the laser beam is set to the recording power (Pw0′) during theperiod T_(top) from the time t₈₁ to the time t₈₂ and the period T_(lp)from the time t₈₇ to the time t₈₈, set to the recording power (Pw0)during the periods T_(mp) corresponding to those from the time t₈₃ tothe time t₈₄, from the time t₈₅ to the time t₈₆ and so on, set to thebottom power (Pb0) during the off periods T_(off) corresponding to thosefrom the time t₈₂ to the time t₈₃, from the time t₈₆ to the time t₈₇ andso on and the cooling interval T_(cl) from the time t₈₈ to the time t₈₉,and set to the erasing power (Pe0) during the other periods. Here,although the pulse width T_(top) of the top pulse, the pulse widthT_(mp) of each of the multi-pulses and the pulse width T_(lp) of thelast pulse are not particularly limited, it is preferable to set them to0.15T to 0.3T and particularly preferable to set them to 0.2T. Further,although the off interval T_(off) is not particularly limited, it ispreferable to set it to (1—Tnxt). Here, Tnxt is the pulse width of apulse present immediately before the off interval T_(off) andcorresponds to the pulse width T_(top) of the top pulse or the pulsewidth T_(mp) of the multi-pulse in FIG. 7( c). Therefore, if T_(top) isequal to 0.2, the off interval T_(off) is equal to 0.8 and if T_(mp) isequal to 0.2, the off interval T_(off) is equal to 0.8. Further,although the cooling interval T_(cl) is not particularly limited, it ispreferable to set it to 0.8T to 1.2T and particularly preferable to setit to about 1.0T.

Thus, at a region where one of a 2T signal to an 8T signal is to berecorded, the L0 recording film 22 melted by irradiation with the laserbeam of the recording power (Pw0) and/or the recording power (Pw0′) isquickly cooled during the cooling interval T_(cl) and the phase thereofis changed to the amorphous phase. On the other hand, at the otherregions, the L0 recording film 22 is heated to a temperature equal to orhigher than the crystallization temperature thereof and lower than themelting point thereof and gradually cooled as the laser beam moves away,thereby being crystallized.

The pulse train patterns described above are those used for recordingdata in the L0 recording film 22. In this manner, in this embodiment, inthe case of recording data in the L0 recording film 22 close to thelight incidence plane 13 a, since the recording powers of the top pulseand last pulse are set to the recording power (Pw0′) lower than therecording power (Pw0) of each of the multi-pulses, it is possible toreduce thermal interference in the L0 recording film 22 in which thecooling effect is low and prevent the L0 recording film 22 from beingre-crystallized.

It is preferable to store information for identifying the pulse trainpatterns for the L0 layer 20 and the L1 layer 30 as “recording conditionsetting information” in the optical recording medium 10. If suchrecording condition setting information is stored in the opticalrecording medium 10, then when data are actually recorded in the opticalrecording medium 10 by the user, the recording condition settinginformation is read by an information recording apparatus and the pulsetrain patterns can be determined based on the thus read recordingcondition setting information. Therefore, for example, when the userrequests recording of data in the L1 layer 30, the information recordingapparatus records data using the pulse train patterns shown in FIG. 6and when the user requests recording of data in the L2 layer 20, theinformation recording apparatus records data using the pulse trainpatterns shown in FIG. 7.

It is more preferable for the recording condition setting information toinclude not only information required for identifying the pulse trainpatterns for the L0 layer 20 and the L1 layer 30 but also informationrequired for identifying various conditions such as the linear recordingvelocity required to record data in the optical recording medium 10. Therecording condition setting information may be recorded in the opticalrecording medium 10 as a wobble signal or pre-pits, or it may berecorded as data in the L0 recording film 22 and/or the L1 recordingfilm 32. Further, the recording condition setting information mayinclude not only information directly indicating various conditionsrequired to record data but also information capable of indirectlyidentifying the pulse train patterns by specifying any of variousconditions stored in the information recording apparatus in advance.

FIG. 8 is a schematic drawing of the major components of an informationrecording apparatus 50 for recording data in the optical recordingmedium 10.

As shown in FIG. 8, the information recording apparatus 50 is equippedwith a spindle motor 52 for rotating an optical recording medium 10, anoptical head 53 for shining a laser beam onto the optical recordingmedium 10, a controller 54 for controlling the operation of the spindlemotor 52 and the optical head 53, a laser driving circuit 55 thatsupplies a laser driving signal to the optical head 53, and a lensdriving circuit 56 that supplies a lens driving signal to the opticalhead 53.

Moreover, as shown in FIG. 8, the controller 54 includes a focusingservo circuit 57, a tracking servo circuit 58, and a laser controlcircuit 59. When the focusing servo circuit 57 is activated, the focusis aligned with the recording surface of the rotating optical recordingmedium 10, and when the tracking servo circuit 58 is activated, the spotof the laser beam begins to automatically track the eccentric signaltrack of the optical recording medium 10. The focusing servo circuit 57and tracking servo circuit 58 are provided with an auto gain controlfunction for automatically adjusting the focusing gain and an auto gaincontrol function for automatically adjusting the tracking gain,respectively. In addition, the laser control circuit 59 is a circuitthat generates the laser driving signal supplied by the laser drivingcircuit 55 and generates a laser driving signal based on recordingcondition setting information recorded on the optical recording medium10.

Note that the focusing servo circuit 57, tracking servo circuit 58 andlaser control circuit 59 need not be circuits incorporated in thecontroller 54 but can instead be components separate of the controller54. Moreover, they need not be physical circuits but can instead beaccomplished by software programs executed in the controller 54.

In the case of recording data in the optical recording medium 10 usingthe thus constituted information recording apparatus 50, as describedabove, the recording condition setting information recorded in theoptical recording medium 10 is read and pulse train patterns aredetermined based on the thus read recording condition settinginformation. Therefore, in the case of recording data in the L1 layer30, the information recording apparatus 50 records data using the pulsetrain patterns shown in FIG. 6 based on the thus read recordingcondition setting information and in the case of recording data in theL0 layer 20, the information recording apparatus 50 records data usingthe pulse train patterns shown in FIG. 7 based on the thus readrecording condition setting information.

The present invention is in no way limited to the aforementionedembodiment and various modifications are possible within the scope ofthe invention as recited in the claims, and these are naturally includedwithin the scope of the invention.

For example, in the preferred embodiment set out above, an opticalrecording medium having two recording layers was described, but theoptical recording media to which the present invention can be appliedare not limited thereto and the present invention is also applicable tooptical recording media having three or more recording layers. In thiscase, when at least one recording mark is formed in the informationrecording layer closest to the light incidence plane 13 a to record datatherein, it is sufficient to set the recording powers of the top pulseand the last pulse to be lower than that of each of the multi-pulses.

Further, in the preferred embodiment above, the pulse train patternswhen the (1,7)RLL modulation scheme was employed were referred to.However, the present invention is not limited to the pulse trainpatterns used when the (1,7)RLL modulation scheme is employed and canalso be applied to the pulse train patterns used when the 8/16modulation scheme capable of recording any one of a 3T signal to an 11Tsignal and 14T signal is employed.

Furthermore, in the preferred embodiment above, the power of the laserbeam is modulated between four levels (four values) of a recording power(Pw0), a recording power (Pw0′), an erasing power (Pe0) and a bottompower (Pb0) in the case of recording information in the L0 layer 20 andthe explanation was made as to the case where the recording powers wereset to two values (Pw0) and (Pw0′). However, the laser power modulatingformat to which the present invention applies is not limited thereto andit is possible to record information by modulating the power of a laserbeam between five levels or more or setting recording powers to threevalues or more, for example.

Moreover, in the preferred embodiment above, the recording powers of thetop pulse and/or the last pulse are set to Pw0′ in the case of recordinginformation in the L0 layer 20. However, it is not absolutely necessaryto set the recording power of a top pulse and the recording power of alast pulse to the same level and they may be set different. Further,only one of the recording powers of a top pulse and a last pulse may beset to be lower than the recording power of each of the multi-pulses. Inconclusion, it is sufficient to set the recording powers of a top pulseand/or a last pulse of a laser beam to be lower than that of each of themulti-pulses in the case of recording information in the informationrecording layer closest to the light incidence plane 13 a.

As described above, according to the present invention, since it ispossible to reduce re-crystallization due to thermal interference,recording marks having good shapes can be formed.

Here, the influence of thermal interference becomes pronounced as thewavelength of the laser beam used for recording data is shorter and thenumerical aperture (NA) of the objective lens used for converging thelaser beam is larger. Therefore, the present invention is particularlyeffective in the case where the quotient (λ/NA) of the wavelength λ ofthe laser beam used for reproducing data divided by the numericalaperture (NA) of the objective lens used to focus the laser beam isequal to or shorter than 700 nm, for example, where the numericalaperture NA is 0.7 (particularly, roughly 0.85) and the wavelength λ ofthe laser beam is about 200 to 450 nm.

WORKING EXAMPLE

Hereinafter, a Working Example will be described concretely.

Fabrication of an Optical Recording Medium 10

A stamper 40 shown in FIG. 2 was first used to perform injection moldingof polycarbonate, thereby fabricating a substrate 11 having grooves 11 awhose depth was 34 mm and whose pitch was 0.32 μm and a thickness of 1.1mm.

Then, the substrate 11 was set in a sputtering apparatus (not shown) andan Ag alloy, a mixture of ZnS and SiO₂ (mole ratio of 80:20), AgSbTeGeand a mixture of ZnS and SiO₂ (mole ratio of 80:20) were sputtered inthis order on nearly the entire surface of the side of the substrate 11on which the grooves 11 a and the lands 11 b were formed, therebyforming an L1 layer 30, namely, a reflective film 34 having a thicknessof 100 nm, a fourth dielectric film 33 having a thickness of 15 nm, anL1 recording film 32 having a thickness of 12 nm and a third dielectricfilm 31 having a thickness of 80 nm.

Next, the substrate 11 formed with the L1 layer was picked out from thesputtering apparatus and an ultraviolet ray curable resin was appliedonto the third dielectric film 31 using a spin coating process. Further,an ultraviolet ray was shined on the surface of the spin-coatedultraviolet ray curable resin through a stamper 41 in the state with itssurface covered with the stamper 41, thereby forming an intermediatelayer 12 having grooves 12 a whose depth was 34 mm and whose pitch was0.32 μm and a thickness of 20 μm.

Then, the substrate 11 formed with the L1 layer 30 and the intermediatelayer 12 was set in the sputtering apparatus and Al₂O₃, SbTe and amixture of ZnS and SiO₂ (mole ratio of 80:20) were sputtered in thisorder on nearly the entire surface of the side of the intermediate layer12 on which the grooves 12 a and the lands 12 b are formed, therebyforming an L0 layer 20, namely, a second dielectric film 23 having athickness of 70 nm, an L0 recording film 22 having a thickness of 8 nmand a first dielectric film 21 having a thickness of 60 nm.

Further, after the substrate 11 formed with the L1 layer 30, theintermediate layer 12 and the L0 layer 20 was picked out from thesputtering apparatus, an ultraviolet ray curable resin was applied ontothe first dielectric film 21 using a spin coating process and anultraviolet ray was shined on the spin-coated ultraviolet ray curableresin, thereby forming a light transmission layer 13 having a thicknessof 100 μm. Thus, an optical recording medium precursor was fabricated.

Next, the optical recording medium precursor was placed upon the rotarytable of a laser irradiation apparatus (not shown) and rotated whilebeing continuously irradiated with a rectangular laser beam having ashorter length in the direction along the track and a longer length inthe direction perpendicular to the track. The irradiation position wasshifted in the direction perpendicular to the track each time theoptical recording medium precursor made one revolution, therebycrystallizing substantially the entire surface of the L0 recording film22 and the L1 recording film 32. Thus, an optical recording medium 10 tobe used in this Working Example was completed.

Recording Data (Measuring a Single Jitter Value)

Random signals including a 2T signal to an 8T signal were recorded onone track of the L0 layer 20 of the thus fabricated optical recordingmedium 10 using the double value recording pulse train patterns shown inFIGS. 7( a) to 7(d). In the pulse train patterns, the recording power(Pb0′), the erasing power (Pe0) and the bottom power (Pb0) were set to0.9×Pw0, 1.5 mW and 0.1 mW, respectively, while the recording power(Pw0) was varied. T_(top), T_(mp) and T_(lp) were set to 0.2T, T_(off)was set to 0.8T and T_(cl) was set to 1.0T.

Further, as a comparative example, random signals including a 2T signalto an 8T signal were recorded on one track of the L0 layer 20 of theoptical recording medium 10 using the single value recording pulse trainpatterns used for recording data in the L1 layer 30 and shown in FIGS.6( a) to 6(d). In the pulse train patterns, the erasing power (Pe0) andthe bottom power (Pb0) were set to 1.5 mW and 0.1 mW, respectively,while the recording power (Pw0) was varied. T_(top), T_(mp) and T_(lp)were set to 0.2T, T_(off) was set to 0.8T and T_(cl) was set to 1.0T.These pulse train patterns were the same as those used for recordingdata in the L1 layer 30 and employed for comparing the case where datawere recorded in the L1 layer 30 using the above pulse train patternsand a case where data were recorded in the L0 layer using the same.

As the random signals, signals in the (1,7) RLL modulation scheme wererecorded by setting the clock frequency to 65.7 MHz (T=15.2 nsec) andthe linear recording velocity to 5.7 m/sec. The wavelength of the laserbeam used for recording data was 405 nm and the numerical aperture ofthe objective lens used for converging the laser beam was 0.85.

Reproducing Data

Each of the random signals recorded in the L0 layer 20 was reproduced bysetting the reproducing power (Pr0) of the laser beam at 0.5 mW, and thejitter and C/N (carrier/noise ratio) of each reproduced signal weremeasured. The jitter was calculated based on the formula: σ/Tw (%) whereTw was one clock period by measuring clock jitter using a time intervalanalyzer and obtaining the fluctuation σ of the reproduced signal. Inthis specification, the jitter value of the signal recorded on the onetrack is sometimes referred to as “a single jitter value.”

FIG. 9 is a graph showing the thus measured single jitter values,wherein the ● mark shows the results of the one value recording and the▴ mark shows the results of double value recording. As shown in FIG. 9,in the case where the recording power Pw0 was equal to or lower thanabout 5.0 mW, since the power of the laser beam was insufficient, thecurve showing the variation of the jitter value of the double valuerecording had the same gradient as that of the single value recordingbut was slightly shifted to the right and the jitter value of the singlevalue recording was lower than that of the double value recording.

However, as the recording power Pw0 was increased above 5.0 mW, thejitter value of the double value recording reached about 12% of a bottomvalue and as the recording power Pw0 was further increased, the jittervalue of the double value recording stayed low because thermalinterference was suppressed, while the jitter value of the single valuerecording became worse because of thermal interference.

It was thus found that in the case of employing the pulse train patternsof the double value recording, the jitter value at a higher recordingpower was lower than that in the case of employing the pulse trainpatterns of the single value recording and that in the case of employingthe pulse train patterns of the double value recording, the range of therecording power Pw0 which could suppress the jitter value to 12% orlower, for example, was wider than in the case of employing the pulsetrain patterns of the single value recording. Therefore, it was foundthat when the pulse train patterns of the double value recording wereemployed, thermal interference on neighboring recording marks could besuppressed and the power margin could be widened.

Recording Data (Measuring a Cross Jitter Value)

Next, random signals including a 2T signal to an 8T signal were recordedon five tracks of the L0 layer 20 of the optical recording medium 10using the double value recording pulse train patterns shown in FIGS. 7(a) to 7(d). More specifically, random signals were first recorded onpairs of two tracks on the opposite side and finally, random signalswere recorded on a central track. In the pulse train patterns, therecording power (Pw0′), the erasing power (Pe0) and the bottom power(Pb0) were set to 0.9×Pw0, 1.5 mW and 0.1 mW, respectively, while therecording power (Pw0) was varied. T_(top), T_(mp) and T_(lp) were set to0.2T, T_(off) was set to 0.8T and T_(cl) was set to 1.0T.

Further, as a comparative example, random signals including a 2T signalto an 8T signal were recorded on five tracks of the L0 layer 20 of theoptical recording medium 10 using the single value recording pulse trainpatterns used for recording data in the L1 layer 30 and shown in FIGS.6( a) to 6(d). In the pulse train patterns, the erasing power (Pe0) andthe bottom power (Pb0) were set to 1.5 mW and 0.1 mW, respectively,while the recording power (Pw0) was varied. T_(top), T_(mp) and T_(lp)were set to 0.2T, T_(off) was set to 0.8T and T_(cl) was set to 1.0T.

As the random signals, signals in the (1,7) RLL modulation scheme wererecorded by setting the clock frequency to 65.7 MHz (T=15.2 nsec) andthe linear recording velocity to 5.7 m/sec. The wavelength of the laserbeam used for recording data was 405 nm and the numerical aperture ofthe objective lens used for converging the laser beam was 0.85.

Reproducing Data

Each of the random signals recorded on the central track of the L0 layer20 was reproduced by setting the reproducing power (Pr0) of the laserbeam at 0.5 mW, and the jitter and C/N (carrier/noise ratio) of eachreproduced signal were measured. The jitter was calculated based on theformula: ρ/Tw (%) where Tw was one clock period by measuring clockjitter using a time interval analyzer and obtaining the fluctuation σ ofthe reproduced signal. In this specification, the jitter value of thesignal recorded on the central track among the five tracks is sometimesreferred to as “a cross jitter value.”

FIG. 10 is a graph showing the thus measured cross jitter values,wherein the ● mark shows the results of the one value recording and the▴ mark shows the results of double value recording. As shown in FIG. 10,in the case where the recording power Pw0 was equal to or lower thanabout 5.0 mW, since the power of the laser beam was insufficient, thecurve showing the variation of the jitter value of the double valuerecording had the same gradient as that of the single value recordingbut was slightly shifted to the right and the jitter value of the singlevalue recording was lower than that of the double value recording.

However, as the recording power Pw0 was increased above 5.0 mW, thejitter value of the double value recording reached about 13% of a bottomvalue and as the recording power Pw0 was further increased, the jittervalue of the double value recording stayed low because thermalinterference was suppressed, while the jitter value of the single valuerecording became worse because of thermal interference.

It was thus found that in the case of employing the pulse train patternsof the double value recording, the jitter value at a higher recordingpower was lower than that in the case of employing the pulse trainpatterns of the single value recording and that in the case of employingthe pulse train patterns of the double value recording, the range of therecording power Pw0 which could suppress the jitter value to 13% orlower, for example, was wider than in the case of employing the pulsetrain patterns of the single value recording. Therefore, it was foundthat when the pulse train patterns of the double value recording wereemployed, the influence of recording marks on neighboring tracks couldbe suppressed, thereby preventing cross-talk of data and cross-erase ofdata and the power margin could be widened.

Thus, it was found that in the case of recording data in the L0 layer 20close to the light incidence plane 13 a, when the recording powers ofthe top pulse and the last pulse were set to be lower than that of eachof the multi-pulses, signal characteristics of the thus formed recordingmarks could be improved.

1. An information recording method for recording information in anoptical recording medium having at least first and second informationrecording layers, the method comprising: projecting a pulse-like laserbeam whose power is modulated between a plurality of levels, includingat least a recording power, onto the optical recording medium via alight incidence plane; forming on the optical recording medium aplurality of recording marks selected from a group that includes severaltypes of recording marks with different lengths; setting recordingpowers of a top pulse and/or a last pulse of the laser beam used when atleast one recording mark is to be formed in the first informationrecording layer to be lower than a recording power of a multi-pulsethereof, thereby recording information in the first informationrecording layer, wherein the first information recording layer islocated on a side of the light incidence plane with respect to thesecond information recording layer and the second information recordinglayer is irradiated with the laser beam via the first informationrecording layer; and recording information in the second informationrecording layer with the recording powers of the top pulse and/or thelast pulse of the laser beam set to be substantially same as therecording power of the multi-pulse thereof.
 2. The information recordingmethod in accordance with claim 1, wherein a wavelength (λ) of the laserbeam and a numerical aperture (NA) of an objective lens satisfy acondition that the wavelength divided by the numerical aperture (λ/NA)is equal to or less than 700 nm.
 3. The information recording method inaccordance with claim 1, wherein the laser beam has a wavelength (λ) ofbetween 200 to 450 nm.
 4. An information recording apparatus forrecording information in an optical recording medium having at leastfirst and second information recording layers, the information recordingapparatus comprising: an optical head adapted to project a pulse-likelaser beam, wherein information is recorded on said optical recordingmedium by projecting said pulse-like laser beam, having power modulatedbetween a plurality of levels including at least a recording power, ontothe optical recording medium via a light incidence plane and forming onthe optical recording medium a plurality of recording marks selectedfrom a group that includes several types of recording marks havingdifferent lengths; and a laser control circuit adapted to set recordingpowers of a top pulse and/or a last pulse of the laser beam used wheninformation is to be recorded in the first information recording layerto be lower than a recording power of a multi-pulse thereof, wherein thefirst information recording layer is located on a side of the lightincidence plane with respect to the second information recording layerand the second information recording layer is irradiated with the laserbeam via the first information recording layer, wherein information isrecorded in the second information recording layer with the recordingpowers of the top pulse and/or the last pulse of the laser beam set tobe substantially same as the recording power of the multi-pulse thereof.5. The information recording apparatus in accordance with claim 4,wherein a wavelength (λ) of the laser beam and a numerical aperture (NA)of an objective lens satisfy a condition that the wavelength divided bythe numerical aperture (λ/NA) is equal to or less than 700 nm.
 6. Theinformation recording apparatus in accordance with claim 4, wherein thelaser beam has a wavelength (λ) of between 200 to 450 nm.
 7. An opticalrecording medium, comprising: at least first and second informationrecording layers in which information can be recorded by projecting apulse-like laser beam whose power is modulated between a plurality oflevels, including at least a recording power, onto the optical recordingmedium via a light incidence plane and forming on the optical recordingmedium a plurality of recording marks selected from a group thatincludes several types of recording marks having different lengths,wherein recording powers of a top pulse and/or a last pulse of the laserbeam used when information is to be recorded in the first informationrecording layer are set to be lower than a recording power of amulti-pulse thereof, wherein the first information recording layer islocated on a side of the light incidence plane with respect to thesecond information recording layer and the second information recordinglayer is irradiated with the laser beam via the first informationrecording layer, wherein information is recorded in the secondinformation recording layer with the recording powers of the top pulseand/or the last pulse of the laser beam set to be substantially same asthe recording power of the multi-pulse thereof.
 8. The optical recordingmedium in accordance with claim 7, further comprising a lighttransmission layer having a thickness of between 30 to 200 μm.